The present invention relates to a method and apparatus for the production of reaction mixtures from liquid reaction components for the production of foam materials.
In order to induce cell formation in the foaming reaction, a specific quantity of a gas, such as air, must be contained in the reaction mixture in the form of fine bubbles which serve as nuclei in the foaming reaction. Depending on the varying desired foam materials a varying quantity of gas is required for this nucleus formation.
For this purpose, a gas such as air is introduced into one of the reaction components which carries the gas with it into the mixing chamber or the gas is introduced directly into the mixing chamber. The first mentioned method has been carried out in the past because in the decompression of the component charged with gas in the mixing chamber, the gas is distributed better. The term "gas charge" of the reaction component is used. This is understood to mean the quantity of gas which is contained in the reaction component in the form of undissolved, finely distributed gas bubbles.
Air or other gas may be introduced into a reaction component (in the case of polyurethane foamable reaction mixtures preferably into the polyol component) for example, by means of a mixing lance or by means of a fast running agitator in the storage container. Gas or air may also be added through porous metal plates or injection nozzles via a dosing device into the reaction component or into a premixing chamber. Finally the components may also be circulated by means of pumps and the return flow is introduced into the gas chamber of the storage container which is under supply pressure and thus absorbs gas.
All these methods are extremely inaccurate and uncertain and hitherto have been carried out purely according to trial and error. Therefore, in previous methods, control of the gas was extremely unstable. The only control was the visual evaluation of the finished product. If, in structural hard cellular plastic the color was dark brown, then it contained too little gas. If the color was light brown, the gas proportion had been correctly selected. If it was light brown with surface bubbles then it contained an excess of gas.
The object of the present invention is therefore to provide a method and apparatus with which the gas charge is measurable, i.e., measurable so as to be reproducible.
In addition, where possible, the gas charge should be automatically controllable.